Phantom island sets news feeds abuzz... except it's real

Strebe

Posted 23 November 2012 - 08:54 PM

Strebe

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Interests:Map projections. Snobby chocolate. Science in general.

United States

A research team claims to have undiscovered a large island in the South Pacific’s Coral Sea near New Caledonia, called Sandy Island. Unfortunately, I have rediscovered it, and so can you. This is a farce. There is, in fact, a massive sand bar at or just below sea level at the location the crew of the RV Southern Surveyor claims to show a depth of 1,400 m. I can confirm this by referencing multiple, independent data sources, including satellite imagery, bathymetry data from multiple sources, and shoreline vector data from multiple sources.† Of course Wikipedia has picked up on this with a dizzying churn of edits in one day. Amusingly it’s all just a big misunderstanding and eventually will be revealed to be so.Example of a news media articleWikipedia article

So, the question is: How did this misunderstanding arise? I don’t think a datum mismatch can account for it; the sand bar is 30 km × 6 km in extent.

Regards,— daan

†

World Vector Shoreline

World Databank II

NASA Blue Marble satellite imagery

SRTM30 Plus, with bathymetry consisting of the Smith & Sandwell global grid, the DLEO Ridge Multibeam Synthesis Project, the JAMSTEC Data Site for Research Cruises, and the NGDC Coastal Relief Model

TenToTwo

Posted 25 November 2012 - 04:16 PM

TenToTwo

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Germany

I was surprised by this as well, mainly because of the mismatch between commonly available bathymetric data and the reported depth of 1400 m at the site of Sandy Island. However, I think the reports are correct, there really is no Sandy Island at that location (even though it's been mapped as early as 1908, http://blog.auckland...hat-isnt-there/)

The research mission was undertaken by oceanographers using a research vessel that is well equipped for bathymetry measurements (http://www.marine.cs...edocs/index.htm, voyage number SS2012_v06). It's very unlikely that they would get their location and the depth soundings wrong.

Also, if you just take a look at the Landsat images of the area, you'll clearly see that there's no island. The Landsat images should be considered most reliable because unlike the Blue Marble images they aren't composed from many different images using a Land/Sea mask. You can browse the images at http://landsatlook.usgs.gov/: Navigate to the area, zoom in on the island (which is present on the orientation map), and click "Select Scenes". You can compare images taken on different occasions, and they all show empty ocean.

Of the sources you quote, two aren't independent: World Vector Shoreline and World Databank II are both derived from other maps and charts, and it's very likely that they used the same source for the region in question.

The NASA Blue Marble imagery shows something that could be taken to look a bit like an island (http://www.blue-marb...5...ay=0&base=0), but I think it's just an artefact stemming from the fact that the land/sea mask to generate the composite image also includes Sandy Island.

The bathymetry in the Smith & Sandwell global grid at the location in question comes from satellite altimetry, the most indirect and imprecise form of depth measurement. There is no multibeam ship track at the location. So I'd say that the bathymetry in this area and in this dataset is just wrong.

mcallisterw

Posted 30 November 2012 - 12:36 PM

mcallisterw

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United Kingdom

I think it's reassuring to know that the world isn't as connected and charted as it sometimes seems, and in the twentieth century we still have to dispatch a ship to a set of coordinates to establish whether or not there is an island there